LOGARITHMIC AMPLIFIER RECTIFIER CIRCUIT AND AGC CIRCUIT FOR TELEPHONE SET USING THE AMPLIFIER RECTIFIER CIRCUIT

摘要

PURPOSE:To employ a low voltage power supply for the circuit by forming the circuit with a differential amplifier receiving a voice signal, a transistor(TR) whose base connects to an output of the differential amplifier and whose collector is used as an output terminal, a diode forming a feedback loop to one end of the input of the differential amplifier from the collector of the TR and a resistor connecting to one end of the input of the differential amplifier to adjust the gain. CONSTITUTION:When a voice input signal is inputted to a voice signal input terminal 1 to bring the level to be more negative than a ground potential, the signal is inputted to a noninverting input terminal of a differential amplifier 3 and an output of the differential amplifier 3 goes to a negative level. At that time, a collector current flows to a TR 4 whose base connects to an output terminal of the differential amplifier 3 and the current flows to a diode 5 connecting to a feedback loop so that the potential of the noninverting input terminal of the differential amplifier 3 is equal to a potential of the inverting input terminal. When a negative voltage is inputted to the voice signal input terminal 1 in this way, the signal is logarithmically amplified resulting that a positive voltage is outputted, and when a positive voltage is inputted to the input terminal 1, the TR 4 is turned off and its output is not less than the ground potential but the positive signal is half-wave-rectified.